Surface properties of mussel adhesive protein component films.

Mussel adhesive protein (MAP) is the adhesive agent used by the blue sea mussel (Mytilus edulis) to attach the animal to various underwater surfaces. It is composed of 75-->85 repeating decameric units with the reported primary sequence NH2-A(1)-K(2)-P(3)-S(4)-Y(5)-Hyp(6)-Hyp(7)-T(8)-DOPA(9)-K(10)-COOH. This study identifies and compares the surface properties of the decameric unit, selected fragments and individual amino acid constituents with the complete MAP preparation. These molecular systems were examined: (a) in the solid state as thin films formed on germanium substrata using multiple-attenuated-internal-reflectance infrared (MAIR-IR) spectroscopy, ellipsometry and contact angle analysis; and (b) in the solution state using circular dichroism (CD) spectroscopy. Extensive molecular modelling of the decamer was performed making integral use of the experimentally derived data. These cumulative semi-empirical and empirical results suggest a conformation for the decamer that closely associates the L-DOPA and tyrosine residues with the solid substratum. This model provides the first representation of MAP derived from a rational integration of theoretical and experimental data. On the basis of this model, a possible explanation for the bioadhesive properties of MAP is suggested.